A flash memory device having a pipelined RAS/CAS architecture is logically organized as an array of rows and columns of multi-bit flash memory cells each capable of being selectively programmed to have a threshold voltage corresponding to one of a plurality of multi-bit bit-sets. In one embodiment, the memory device is adapted to perform a burst read operation in which a row of flash memory cells is sensed and latched and subsequently outputted from the device on consecutive clock cycles following a sense latency period. In accordance with one aspect of the invention, the pipelined architecture allows for a second burst read operation to be initiated prior to completion of the first, such that the sense latency periods for all but the first of a series of successive burst read operations are hidden, enabling the memory device to perform comparably to a memory device having conventional flash memory cells.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method of operating a semiconductor memory device having multi-bit non-volatile memory cells, comprising: activating a first read utilizing a first command, the first read addressing a first plurality of multi-bit non-volatile memory cells; sequentially outputting first multi-bit outputs for each of the first plurality of addressed multi-bit non-volatile cells; activating a second read utilizing a second command, the second read addressing a second plurality of multi-bit non-volatile memory cells; and sequentially outputting second multi-bit outputs for each of the second plurality of addressed multi-bit non-volatile cells, wherein the second multi-bit outputs are output immediately after the first multi-bit outputs without latency.
2. The method of claim 1 , wherein first and second commands comprise sequences of signals applied externally to the device.
3. The method of claim 2 , wherein the latency between the signals in each command is sufficiently long to resolve the status of the multi-bit outputs for each of the plurality of multi-bit flash cells.
4. The method of claim 1 , wherein the second read is activated simultaneously with outputting the first multi-bit outputs.
5. The method of claim 1 , wherein the first and second commands are both accompanied by an application of an externally-applied row address and an externally-applied column address to the memory device.
6. The method of claim 1 , wherein values of the first and second multi-bit outputs for each flash cell corresponds to four threshold voltages for each flash cell.
7. The method of claim 1 , wherein the first or second plurality of multi-bit flash cells are formed in a single row of the memory device.
8. The method of claim 1 , wherein the first and second commands comprise signals applied externally to the memory device.
9. The method of claim 1 , wherein the first and second commands are synchronous with a clock signal applied externally to the memory device.
10. The method of claim 1 , wherein the multi-bit outputs are output in synchronization with a clock signal applied externally to the memory device.
11. The method of claim 1 , wherein the multi-bit non-volatile memory cells comprise multi-bit flash memory cells.
12. A method of operating a semiconductor memory device comprising an array of rows and columns of non-volatile memory cells, comprising: programming a plurality of the non-volatile memory cells to more than two possible threshold voltages, wherein the more than two threshold voltages each correspond to multi-bit bit-sets; in response to a first command, sensing the threshold voltages of the plurality of memory cells along a row of the memory device to form read data; and in response to a second command, sequentially outputting the read data starting at a particular column along the row.
13. The method of claim 12 , wherein the first command comprises a Row Address Strobe signal to the memory device.
14. The method of claim 12 , wherein the second command comprises a Column Address Strobe signal to the memory device.
15. The method of claim 12 , wherein the method comprises programming the plurality of the non-volatile memory cells to four possible threshold voltages, and wherein the four possible threshold voltages correspond to two-bit bit-sets.
16. The method of claim 12 , wherein a latency between the first command and the second command is sufficiently long translate each sensed threshold voltage into its multi-bit bit-sets.
17. The method of claim 12 , wherein the first and second commands are synchronous with a clock signal applied externally to the memory device.
18. The method of claim 12 , wherein the read data is output in synchronization with a clock signal applied externally to the memory device.
19. The method of claim 12 , wherein the non-volatile memory cells comprise flash memory cells.
20. The method of claim 12 , further comprising latching the read data in a latch prior to outputting the read data in response to the second command.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
February 21, 2006
June 26, 2007
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